1. Field of the Invention
This invention relates to aircraft guidance systems and, more particularly, to a visual approach system for guiding an aircraft to a runway along a precisely located glide slope and course.
2. Description of the Prior Art
During the approach of an aircraft to the runway for landing, it is essential that the pilot maintain the aircraft at the appropriate angle with respect to his intended point of touchdown on the runway. This line of approach, often referred to as the glide slope or glide path, must be maintained substantially constant within relatively narrow limits and the line must be measured with respect to the same given point of expected touchdown. Any material variance from this line of approach may cause the aircraft to strike an obstruction such as a tree or power line, or may cause touchdown of the aircraft on the runway at a point either short of the end of the runway or dangerously far down the runway toward the opposite end thereof as a result of an improperly chosen touchdown point. Similarly, it is necessary for the aircraft to follow a course which is aligned with the center line of the runway to insure a landing on the center of the runway and prevent the aircraft from striking objects which project upwardly on one side of the glide slope.
Conventional techniques have been developed for solving the foregoing problem to some extent. For example, the well-known instrument landing system (ILS) enables the pilot of an airplane to maintain his craft on the proper approach path as defined by appropriate radio beams transmitted from the ground. Also, at airports equipped with ground-controlled approach (GCA) equipment, the pilot can be talked down by the ground controller if the need arises. Both of the foregoing techniques, however, require the presence on the ground of elaborate and expensive equipment, and the ILS system additionally requires the presence in the aircraft of radio receiving apparatus which is expensive and which adds weight to the craft. Because of this, many of the smaller public airports and virtually all private airports are equipped with neither of the aforenamed landing aids. Furthemore, a substantial number of smaller aircraft are not equipped with ILS apparatus because of the added expense of such apparatus.
Although choosing and flying the proper approach path presents no particular problem to the skilled pilot during VFR (visual flying regulations) conditions, nighttime landings for the pilot whose plane is not equipped with ILS or who is landing at an airport having neither ILS nor GCA equipment presents a very real hazard. The magnitude of this hazard may be increased when the pilot is landing at a field having only relatively rudimentary lighting.
While various means have been devised which cause the pilot to see differing illumination patterns and/or colors depending on his position relative to the proper approach path and course, such means have been relatively expensive, unwiedly or otherwise unsuited to the needs of small airports.